BRAINCAKESoap Making
Soap is made by the alkaline hydrolysis of vegetable oils and animal fats. The fat or oil is heated with concentrated aqueous sodium hydroxide. Each of the three ester groups in the triglyceride is hydrolysed, giving propane-1,2,3-triol (glycerol) and the sodium salts of the long-chain carboxylic acids. These salts are soap.
triglyceride + 3NaOH → CH2(OH)CH(OH)CH2OH + 3RCOO−Na+
For example, if every chain is C17H35, the soap is sodium octadecanoate (sodium stearate), C17H35COO−Na+. Using potassium hydroxide instead gives potassium salts, which make softer soaps.
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Key terms in this lesson
- triglyceride
- An ester formed from one molecule of glycerol and three fatty acid molecules, found in vegetable oils and animal fats.
More in Carboxylic Acids and Derivatives
- Naming Esters
- Uses of Esters
- Hydrolysis of Esters
- Vegetable Oils and Fats
- Biodiesel
- Acyl Chlorides
- Acid Anhydrides
- Nucleophilic Addition-Elimination Mechanism
All 16 lessons in Carboxylic Acids and Derivatives · All AQA A-level Chemistry topics